The present invention relates to an electric brake and, in more particular, to an electric brake including a pad clearance adjusting mechanism and a method for adjusting the pad clearance of the present electric brake.
Conventionally, in a hydraulic brake, when a pad is worn, there is executed a pad clearance adjustment in which a hydraulic piston provided in the hydraulic brake is automatically moved back at a given amount by a seal so arranged as to hold the hydraulic piston in a fluid tight manner, a clip or the like, so that the clearance of a friction pad provided in the hydraulic brake can be always kept constant.
On the other hand, in an electric brake which has been developed positively in recent years, since a piston provided therein can be operated only in accordance with an instruction from a control device, a pad clearance adjustment in the electric brake is difficult. This urges the development of a technology which is able to automatically execute the pad clearance adjustment.
Here, as an example of a conventional electric brake, description will be given below of an electric brake which is disclosed in Japanese Patent Publication No. Hei. 3-41233 (corresponding to U.S. Pat. No. 5,107,967). This electric brake comprises: a brake disc which is to be connected to a rotary body to be braked; a friction pad which includes a friction surface located opposed to the side surface of the brake disc and can be moved advancingly and retreatingly; a piston for pressing against the back surface of the friction pad when the friction pad advances; a brake caliper which is mounted on a fixed bracket and supports the piston in such a manner that the piston can be moved reciprocatingly; and, a thrust (driving force) generating device which is provided in the brake caliper and generates a thrust to cause the piston to move advancingly, in which the thrust generating device includes an electric motor, a drive shaft connected to the output shaft of the electric motor, a rotary shaft which can be threadedly engaged with the piston through a ball screw, and a reduction gear which is interposed between the drive and rotary shafts and allows the drive shaft to drive the rotary shaft in such a manner that the rotation speed of the rotary shaft can be reduced as compared with that of the drive shaft, characterized in that, between the piston and caliper, there is interposed a slide bearing which, in a braking operation, is used to receive a side thrust applied to the piston from the friction pad.
However, in the above-structured electric brake, because the piston can be moved only in accordance with a brake instruction from a control device, when the brake pad is worn, it is not possible to automatically adjust the clearance of the brake pad as in the conventionally known hydraulic brake. Due to this, it is difficult that the pad clearance can be always set constant. As a result of this, when the brake pad is worn, there cannot be obtained a stable brake feeling.